Effort closure is tighter occlusion of the laryngeal inlet, in which the aryepiglottic muscles contract strongly to act as a sphincter, allowing the airway to withstand up to 120cmH2O of pressure.

Lower Airway

The lower airway consists of the tracheobronchial tree:

From trachea to alveolus, the airways of the lungs divide 23 timesThe tracheobronchial tree is divided into two zones, based on whether they contain alveoli and therefore are able to participate in gas exchange: